Field of the Invention
The present invention relates to an image forming apparatus configured to form a toner image on a recording material through use of an electrophotographic printing method, such as a copying machine, a printer, a fax machine, or a multifunctional apparatus having a plurality of functions thereof.
Description of the Related Art
In an image forming apparatus employing an electrophotographic printing method, a toner image is transferred onto a recording material in a transfer portion, and then is heated and pressurized by a fixing device to be fixed onto the recording material. Regarding such a configuration, in Japanese Patent Application Laid-Open No. H10-97154, there is described an image forming apparatus in which the conveyance speed of a recording sheet in a nip portion (fixing nip portion) of a fixing device is set to be less than that of a recording sheet (recording material) in a transfer portion (transfer nip portion). With this configuration, the recording sheet is prevented from being pulled between the fixing nip portion and the transfer nip portion, to thereby prevent distortion of an image caused by pulling of the recording sheet.
In the image forming apparatus described in Japanese Patent Application Laid-Open No. H10-97154, due to a difference in conveyance speed between the fixing nip portion and the transfer nip portion, the recording sheet has a flexed shape between the fixing nip portion and the transfer nip portion. When the recording sheet is flexed as described above, a force is exerted on an image bearing member that is brought into contact with the recording sheet in the transfer nip portion, in a direction opposite to the rotation direction of the image bearing member due to a rigidity (stiffness) of the recording sheet. When the rotation speed of the image bearing member is changed with such a force, an image defect, such as color misregistration, may be caused.
In view of the foregoing, it is conceivable that the force exerted on the image bearing member due to flexure of the recording material between the transfer nip portion and the fixing nip portion is canceled out by flexing the recording material on an upstream side of the transfer nip portion. When the recording material is brought into contact with the image bearing member at an upstream position of the transfer nip portion in a state in which the recording material is significantly flexed on the upstream side of the transfer nip portion, however, a toner image borne on the image bearing member may be distorted to cause an image defect.